An explosion on a North Philadelphia food truck caused the July 1 fire that killed a mother and daughter and injured nine others, fire officials said today.

The blast, which killed Olga Galdamez, 42, and her daughter Jaylin Landaverry, 27, “was a direct result of a buildup of propane gas discovering an ignition source," said Fire Commissioner Derrick J.V. Sawyer in a statement.

Galdamez owned the popular food truck, called La Parrillada Chapina, on the 300 block of West Wyoming Avenue in Feltonville. Galdamez and Landaverry were closing up for the night when a fireball erupted, sending shrapnel and debris flying for a "substantial distance."

Sawyer said the ignition source could not be determined because the truck had several burners, warmers and pilots. The fire marshal and the Arson Task Force continue to work to discover what caused the release of the propane.